Electric condenser and method for making the same



March 2, 1948. F. D. scHo-r'rLAND ELECTRIC CONDENSER AND METHOD FOR MAKING THE SAME Filed D60. 23, 1942 2 Sheets-Sheet 1 lllllllllllllllll IIIPHIIIIHI March 2, 1948. F. D. scHoTTLAND 2,437,212

ELECTRIC CONDENSER AND METHOD FOR MAKING THE SAME Y Filed Dec. 23, 1942 2 Sheets-Sheet 2 M IIJIU-u ff f/ 7; ////7//////////// /////L 52 lf2? INVENTOR FRED D. SCHOTTLAND ATTORNEY -Jlllllllll-. Hlm-IIN condenser comprising a stack each other 'without the aid of 4 pedients such as clamps,

`vide a condenser 'Patented Mar. 2 A19138 STATES PATENT OFFICE ELECTRIC coNnaNsEa AND Ms'rnon Foa Maxine THE SAME Frederic D. Schottland, Forest Hills, N. Y. ApplicatlonDccembe 23, 1942, Serial No. 469,864 1 2 claims. (ci. irs-41) This invention relates to electric condensers and to a method for making the same. More speciiically, the invention pertains lto condensers of the type which include a plurality of laminae each of which comprises a dielectric sheet havingmetallic deposits on opposite surfaces thereof.

Heretofore these laminas have been singly used in electric circuits. Attempts have been made to assemble a plurality of laminae into a multiple unit which has a larger capacity, a, greatercuror a greater voltage the main object of the present invention, accordingly,- to avoid these drawbacks and vprovide an inexpensive method for ,A making compact and highly emcient condensers .lcomprisinga stack of such laminae.

The laminaeinclude both mica sheets 4and cei ramic plates, th`e tendency being to use ceramic plates because of their'high dielectric constants. In efforts to stack a plurality of ceramic plates several factors have .combined to render the methods employed impractical. Such factors have included the inherently fragile nature of the ceramic plate which prevented the'use of large pressures in holding the stacked plates to gether, the'uneven surfaces of the -ceramic plates which prevented contiguous plates from making plane contact and tended to induce corona discharge'. andl the degradation of power factor ,which has heretofore always resulted when cei H ramic plates of the character underdiscussion were assembled into stacks. other object of the invention mercialiy practical method of It is therefore arito provide a commaking-aI low -loss of coated ceramic plates.

A further object of the invention is to provide i a. condenser comprising a plurality of stacked metalic coated ceramic plates which are held to mechanical excasings, or the like.

An additional object of the invention is to provide a condenser comprising a plurality of stacked.

metallic coated ceramic plates, the coatings of which are autogenously welded to each ether.

t `iet another' object of the invention is to proof the character described wherein laminae including dielectrics having very .high dielectric constants are employed without appreciably deteriorating the power factor of the condenser.

Other objects of the invention will in part be obvlous and in part 'ircreinaittr pointed out.

In the accompanying drawings in which are shown various possible embodiments ofthe invention and wherein like numbers refer to like parts throughout.

Fig. 1 is a perspective view of one condenser lamina. fabricated from a ceramic plate;

Fig. 2 is a rality of condenser laminae stacked in preparation for autogenous welding;

Fig. 3 is a, vertical sectional view through said stack after the same is positioned in a holding mechanism;

Fig. 4 is a schematic view oi' a retort in which several stacks are being autogenously welded;

Fig. 5 is a vertical sectional view through a con` denser constructed in accordancewith and embodying the invention, the several laminae being connected in parallel;

Fig. 6 is a fragmentary perspective view of a special spacer element which is employed when the surfaces oi .the ceramic plates are not absoing a, spacer such as shown in Fig. 6, the laminae in this condenser being connected in series;

Fig. 8 is a vertical sectional view through a condenser embodying a modified form of the invention.

In general I- carry out the objects of the invention by assembling a plurality of metallic coated dielectric plates in stacked relationship and either same. Preferably this is accomplished by raising the metallic coatings te their melting point while pressed against each other. i; e. by autogenous welding.

Referring now in detail to the drawings and more particularly to Figs. 1 through 5, I have there shown a. condenser I0 .(Fig. 5) embodying my invention. Said condenser is made by treating a, desired number of laminae I2 (Fig. 1) in accord-ance with the invention.

Thelaminac I2 may bc contnictcd in any suitable manner well known to the art and may be vertical sectional view through a pluanemia of circular profile although such shape has no bearing on the invention. They each comprise a plate I4 of a suitable dielectric material as for example mica or a. ceramic substance such as titanium dioxide. The illustrated lamina is mainly composed of titanium dioxide and is, therefore, thicker than a sheet of mica. Both the top and bottom surfaces of the plate I ii are partially coated with a metallic deposit which includes a central portion I8 spaced from the rim of the plate I4 to leave a margin I8 therearound. The coating Ialso includes a leg 2d which is integral with and extends away from the central portion I6, spans the margin I8, and extends down and over the plate rim. The depending portions 22 of the legs 20 are for connecting a plurality of the lamina I2 in parallel if desired. The legs 20 on each lamina are connected to central coated portions I6 on opposite surfaces of the ceramic plate It and are anguiarly spaced from each a finely powdered metallic substance.` One such iluid is sold to the trade under the name ISilver Spray No. 4253 by the E. l'. du Pont de Nemours & Co., Inc. The vehicle of this spray is 65% alcohol and 35% water. Thehmetallicwpgwder suspended in the spray is a low meltir'g' silver Vabout 90% by weight oi titaniumjioxid (T102) boundaries of the central portions I6 in perfect registration this will not be possible because of minor discrepancies arising from slight diiferences in the sizes of the plates I4 and slight differences in positioning of the masks during deposit of the. coatings I6. This failure to secure 1 perfect registration .of the boundaries of the central coated portions I8 is believed to be the cause of the poorpower factor heretofore attained when a plurality of laminae of the character described were stacked as shown in Fig. 2 and held in this position by 'an extraneous fastening or clamping means. It is believed that the air gap which existed 'because of the imperfect alignment of the boundaries of a composite dielectric consisting of such air gap and the dielectric plate I4 which have widely difand about 10% by weight of zirconium titana' (ZrTiOs). It will be understood of course that the foregoing speciiic substances and proportions are given by way oi' example only and are in no sense to be construed as a limitation upon the scope of the invention.

It may be mentioned that the peripheral definition oi' the metallic coatings on the upper and lower surfaces is best obtained by employing a mask during spraying oi the ceramic plate.

Although I have described in some detail the method of depositing a metallic substance on the ceramic plate by spraying a powder suspended in a volatile vehicle. it will be understood that other methods of depositing the metallic coating which `are now practiced by the art may alternatively be employed. Such methods include hot metal spraying and electrodeposition.

After a plurality oi lamin'ae I2 have been prepared they are arranged in stacked relationship with the edges of adjacent plates I4 and the boundaries of juxtaposed metallic coated central portions I6 in substantial registration. The legs 20 of juxtaposed central portions -IB are also disposed in alignment, This stacked condition of the several laminae is shown in Fig. 2. It will be appreciated that the illustrated thickness of the'metallic coatings in this figure, as well as in all other iigures of the drawings, is exaggerated for the purpose of illustration, as such coatings are actually too thin to appear in the drawings ifthe same were shown to scale. Particular attention is called to the fact that although attempts may be made to place the ferent dielectric constants. Where such a conditionwas present a tendency to corona dis charge existed and the same, of course, materially degraded the power Vfactor of the condenser. It will be appreciated that as plates having higher and higher dielectric constants are employed the loss in power factorarising from the foregoing condition will become greater and greater so that all the advantages resulting from using a material having a high dielectric constant are lost. Pursuant to my invention the drawback Just described may be overcome and the several laminae self-held to each other by treating the stacked metallic coated laminae I2 in the fol-v lowing manner: g

After the laminae have been stackedas shown. in Fig. 2, they are introduced into a holding mechanism 24 (Fig. 3) which comprises a. ceramicA base 26 having a plurality of circularly arranged upwardly extending ceramic legs 28. The spacing of the legs is such that the rim of the stacked laminas I2 are disposed in a, sliding fit lagainstthe inner surfaces thereof when said laminae are located in the holding mechanism 24. Lugs 30 extend inwardly from the bottom of the legs 28 to maintain the under surface of the lowermost lamina spaced from the base 28. The radial length of said lugs is less than the width of the margins I8 'on said laminae. Furthermore, when the l-aminae are disposed inthe holding 'mechanism the legs 20 includlngthe depending lweight from contacting the central coated portion i6 ofthe uppermost lamina. VA slot 38 is also formed in the bottom surface of the weight to enable the same to clear the leg 20 of said lamina.

A plurality of holding mechanisms 24, each supporting a predetermined number of' stacked laminae, are introduced into Aa suitable heating device, such Afor example as a retort 36, in which the temperature of the laminae is raised by electric resistances 38 to the melting point for'the metallic coatings. A thermostat 4I! isl provided to prevent the temperature from rising too greatly above the melting point and -thus avoids: possible vaporization of the metallic coatings, If desired an inert atmosphere may be maintained inside of the retort during, heating of the condensers whereby to preventoxidization of the molten metallic coatings.

the coating portion I6 produced After the condehsers have beenl brought to the desired temperature they are allowed to cool either inside of or outside of the retort; 38. The structure of said condensers is then such as is illustrated in Fig. 5. All the contiguous metallic coatings including the central portions I6 and legs 2li will be found to have been autogenously welded. Furthermore, the boundaries of the contiguous and now fused metallic coatings will be found to be in perfect registration. This is believed to be due to tliefact that although when in solid state the metallic coatings have a greater affinity for the ceramic plates i4 than for each other, when the metal is in molten condition it has a tendency to agglomerato and this will eliminatc discrepancies in the boundaries between contiguous metallic coatings. This tendency towards agglomeration of two contiguous horizontal molten metal layers is so great that it is believed that the layers near the top of the stacked laminae would reduce in'sizc and increase in thickness were it not for the presence of the weight 32. The mass of said weight should therefore be selected Awith this function in mind. I have found that when the plates are approximately 11/ inches in diameter and aff of one inch in thickness and the compositions of the plate and metallic coatings are as specified earlier in the description, a Weight of about three ounces will give highly satisfactory results. A tendency oi' like degree towards agglomeration does not exist in the vertical portions 22 of the legs which are only of, single thickness.

A condenser constructed in accordance with my invention has an extremely low power loss and the power factor thereof is substantially the same as the power factor of a single lamina. Also because of the simple means for holding the lamina to each other the condenser is of minimum size. employs a minimum of materiaL'and is very rugged. l

The stacked and welded laminae may be connected in series or parallel depending upon the use to which they are to be put. In Fig. 5 I have illustrated said lamina@ as connected in parallel. This is accomplished by securing a pair of leads ft2, dit to the depending portions 22 of the legs 20 on opposite sides of the condenser. The' leads may be secured in any suitable fashion, as forl example by soldering, silver brazing, or by pressing the same against the depending portions 22 during the autogenous welding step practiced in the retort 36.

In the description of the condenser I0 it has been assumed that the upper and lower surfaces of the ceramic plates I4 were substantially plane and parallel by virtue of exercising special care in the production thereof or by subsequently grinding such surfaces. Actually, in the present state of the ceramic art, it is necessary to grind the surfaces. This step, of course, entails a, certain additional expense and may be avoided by employing a modified form of my invention, shown in Figs. 6 and 7.

Under present day manufacturing conditions the deviation from plane condition oi. a ceramic plate I il can easily be kept relatively slight, in the order of a few thousandths of an inch. When stacking plates having such a contour, I introduce between successive plates a spacer element 46 (Fig-g. 6) Said elements are of the same plan outline as the central metallic coated portions Iii but au: of slightly smaller dimensions. 'I'he spacers are made from a metal having a higher melting point than the metal deposited upon the ceramic plates. By way of example, such metal may be pure silver. This metal is coated either by spraying, dipping. or the like with a metallic deposit the same as or similar to that deposited upon the ceramic plates I4. The spacer is corrugated across its entire surface. These corrugations may be of any well known type as for example the transverse corrugations shown, height of the corrugations is at least equal to the maximum deviation from planeness of the fiat surfaces oi.' the ceramic plates I4 for a reason which will soon be apparent. The thickness of the metal comprising the spacer is very slight and may be as little as one third to one half the thicknessof the metallic'coatings so that said spacer. in reality, comprises nothing but a foil barely heavy enough to maintain its own shape when no external pressure is applied, and which will be crushed or deformed when subjected to a pressure as low as that engendered upon imposition oi.' the light weight 32.

l When such spacer elements are inserted between adjacent stacked laminae and the weight 32 placed on top of the stack, the spacers will be crushed where the space between the laminae is at a minimum and will touch the metallic coating I8 where the space between the laminae is -at a maximum. This will insure maintenance of an even potential throughout the entire surface of a metal condenser plate during use. It will also solidify the internal structure of the finished condenser. Most important, it will aid in rectifying boundary discrepancies of contiguous metallic coatings I6. This is best shown in Fig. where the edge of the lowex` spacer 46 is interamediate two ceramiclplates I4, between whose rims more than a. minimum spacing exists. It is believed that the edge of the spacer which, it will be remembered, is spaced inwardly from the boundary of the coating I6, aids in supporting the expanded meniscus which marks the new boundary of the autogenously welded metallic coatings.

It will be appreciated that by using a corrugated spaceri'oil, such as described, instead of an excessive thickness of metallic deposit on the plates I4, I am able to prevent undue flow of the molten metal during autogenous welding, while still maintaining uniform boundaries for the coatings on adjacent ceramic plates, and maintaining said coatings contacted over substantial areas thereof.

Greater unevenness oi surface can be overcome by employing pairs of overlying spacer foils having the corrugations thereof relatively angularly disposed. However. such use is not to be encouraged, as with it boundary discrepancies do not wholly disappear although they are considerably rectified.v

It will be noted that the foil from which the spacer element is fabricated can be a metal which includes at least one element employed in the alloyed metallic coating I6 whereby to create a solid jointupon welding.

In Fig. 8 I have show n a condenser embodying a modified form of my invention and employing an alternative structure for overcoming the irregularity of the upper and lower surfaces of the ceramic plates. Said condenser 5i! comprises a plurality of ceramic plates 52, each of which is provided on its upper and lower surfaces with two concentric rings 54, 56. Both the outer and lnner.ilngs 64. |58 are of the same li'eight. Such height'may be in the order of a few thousandths of an inch and need only be suicient to clear all or waiile or `radial corrugations. The

cascata unevennesses in the surface ci' the 'plate t2. The width oi the rings lit. @t may be the same or different, as desired. The width oi the outer ring should be at least auch that good contact bea tween two contiguous coatings on adjacent plates may be obtained. The width of the inner rings should bel suicient to prevent warping oi the plate t2 during baking. All outer rings are of identical diameter and are identically disposed on the upper and lower surfaces oi the plates 52. The outer rings can be used to define the boundaries of the central coating portions it disposed on the upper and lower surfaces of the plates 52. The plates t2 are also provided with the usual leg portion and depending rim portions such such as are shown in connection with the flat plate it (Fig. 1). Prior to metallic coating of the plates t2, the outer ring bfi and inner ring 56' on each surface are ground down to a common plane. I have found that this operation may be practiced at a relatively low cost and considerably below cost of grinding the entire surface of a fiat ceramic plate it. The'plates 52 are assembled in stacked position with the outer rings 5t as close to identic registration as possible and the coatings on the top oi? said rings are autogenously welded to each.- other in the same manner as that described with reference to the plates it. The contact afforded between two outer rings 5H is ample for the frequency at which most electric circuits are designed to operate so that this forni o! condenser affords a good practical solution for overcoming the dilculty arising from the unevenness of the upper and lower surfaces ci ceramic plates, while at the same time aiding accurate boundary registration of the two central coating portions prior to welding.

It will thus be seen that there are provided a method Iand device which achieve the several objects of this invention and which are well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention andV as various changes might be made in the embodiments above set forth, it is to 'be understood that all matter herein set forth or shown in the accompanylng drawings is to be interpreted as illus trative and not in a limiting sense.

Having thus described my invention I claim as new and desire to secure by Letters Patent:

1. A condenser comprising a plurality of stacked ceramic plates, each of Whose upper and lower surfaces have metallic coatings of similar sizes and shapes thereon, said coatings having boundary edges, the plates being arranged so that .the metallic coatings on juxtaposed faces are in substantial registration. said coatings being fused .together so that the edges thereof are exactly registered.

2. A condenser comprising a plurality of stacked ceramic plates, each of whe upper and lower surfaces have metallic coatings of similar sizes and shapes thereon, said coatings having boundary edges, the plates being arranged .so that the metallic coatings on juxtaposed faces are in substantial registration, the edges of said coatings lbeing fusedly joined so that they are in exact registration.

3. A condenser comprising a plurality of stacked ceramic plates cach of whose upper and lower surfaces have metallic coatings of similar sizes and shapes thereon said coatings having boundary edges, the plates being arranged so that the metallic coat-ings on juxtaposed faces are in the metallic coatings on juxtaposed faces are in substantial registration and the edges of said coatings being exactly registered by metallic welding. v

s. .il condenser comprising a plurality of stacked ceramic plates each of whose upper and lower surfaces have metallic coatings of similar sizes and shapes thereon said coatings'having lboundary edges, the plates being arranged so that substantial registration and the edges of said coatings being exactly registered by autogenous welding.

5. A condenser as set forth in claim 4 wherein the ceramic plates are irregular and wherein a corrugated metallic spacer isdisposed between adjacent metallic coatings, said spacer being of a.

metal having a. fusing point higher than the fusing point of the metallic coatings and being itself coated with a. metallic coating, the height of the corrugations being at least equal tothe greatest deviation from planeness oi the upper or lower surfaces of the ceramic plates.

6. A condenser as set forth in claim 4 wherein the upper and lower surfaces of the ceramic plates each have a ring thereon, said surfaces being coated with metal within and over the top of said rings, the plates being arranged so-that the rings are in alignment.

' '7. A method ot making condensers which include a plurality of ceramic plates each of whose upper and lower surfaces have metallic coatings of similar sizes and shapes thereon said coatings having boundary edges, said method comprising the steps of assembling the plates in stacked relationship with the metallic coatings on juxtaposed surfaces of adjacent plates in substantial registration and then exactly registering the edges oi said coatings by welding the same.

8. A method of making condensers which include .a plurality of ceramic plates each of Whose upper and lower surfaces have metallic coatings of simil-ar sizes and shapes thereon said coatings having boundary edges, said method comprising the steps of assembling the plates in stacked rel-ationship with the metallic coatings on juxtaposed surfaces oi adjacent plates in substantial registration and then exactly registering theedges of said coatings by autogenously welding the same.

9. A method ol! making condensers which include a plurality of ceramic plates each of whose upper and lower surfaces have metallic coatingsl Iof similar sizes and shapes thereon said coatings having boundary edges, said method comprising the steps of assembling the plates in stacked relationship with the metallic coatings on juxtaposed surfaces of adjacent plates in substantial registration and then exactly registering the edges ofA said coatings by heating said stacked plates to the fusion temperature of said coatings.

lll. A method of making' condensers which include a plurality of ceramic plates each of whose upper and lower surfaces have metallic coatings of similar sizes and shapes thereon said coatings having boundary edges, said method comprising the steps of assembling the plates in stacked relationship with the metallic coatings on juxtaposed surfaces of adjacent plates in substantial regls- 4 tration and then exactly registering the edges of said coatings by heating said stacked plates to the fusion temperature oi said coatings while maintaining said stacked plates in compression.

1l. .A method of making condensers which include a. plurality of ceramic plates each of whose upper and lower surfaces have metallic coatings 76 of similar sizes and shapes thereon said coatings :ha g1 boundaryyjedges; saidmcthcd comprising said 4coatings by heating said stacked plates to the t thefstepsjbt assembiinzthe plates instacked rela,` fusion temperature or said coatings but not b'ei `1210111811111"withafizhe'7111112111116v coatings on imitar youd the vaporization temperature thereof. gppse 1 urraces o r-fadacent plates 1n substantial i 'FREDERIC D. sCHo'I'rLAND. xjegis y121110111 and,-t1iex1 exactly registering the s .ed ofsaLidbctnglsgby heatingsid stald REFERENCES CITED 1121# .tolthcgfusicnltemperature g1' s dvcoa s 1 keeping .smd-@sfscked-pmes under s slight m'f ftlllgfgeferems e `f ma m the A mcthod'lffmsakingccndensrs which-infy 10 UNITED STATES PATENTS :clild a pluralityfqf-ceramicipiates each ci.' whose Number Name y Date klipnergand-1owe1-isuriaceshavcmetalliccoatings 1,479,315 pickard Jam 1, 1924, 'QfifSim-ilarisizes and' srwnes thereon said coatings f 1,568,918 .pmner Jan, 5, 1926 1111111.71.xls"bQundaryI edses'.,saidmethod comprising `1,703,816 Pickard Mar. 26, 1929 .itn-esteps of'assembnngvthe plata; in Stacked'l'ela" -15 1,721,503 P11555 July 23, 1929 1515.195511@ With'thmetallclcqatin'gs on juxtaposed 1,311,725 Marckworth June 23, 1931 gsurtcesofadiacntwplatesin substantial resis- 2,141,677' ziegenuaein Dec. 27, 193s ftratipn andfth'enxatly registering the edges of 2,157,715

I Meggenhfen May 9, `1939 

